A multi-technique approach to characterize bioactive silicate composites

In the present work the ternary SiO2·CaO·P2O5composite, which differ in the Ca/P molar ratio, were synthesized by means of a sol-gel route. In order to investigate the influence of the relative amount of each phase the thermal properties of the synthesized gel-glass materials were studied as a function of the Ca/P molar ratio using thermogravimetric and differential thermal analysis (TG/DTA). After dehydration (in a single step), described from a kinetic point of view as a simple water evaporation without rupture of chemical bonds, all gels undergo a complex multi-step decomposition with endo and exothermic effects, followed by crystallization of calcium silicate phases at about 950°C. Furthermore, Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD) and Scanning Electron Microscopy, coupled with energy dispersive spectroscopy (SEM/EDS), allowed us to detect the chemical modifications induced by modifying the Ca/P molar ratio and the sintering. This process is obtained by thermal treatment of the materials after analyzing their thermal behavior in the temperature range 600-1000°C, with the aim of making them suitable for their applications. The results revealed that when temperature is up to 900°C, crystallization occurs and pseudowollastonite and wollastonite were formed. Finally, the amount of pseudowollastonite decreased with increasing the sintering temperature, while that of wollastonite increased

Inertization of mine tailing via cold consolidation in geopolymer matrix

The consolidation via geopolymerisation is a room temperature alkaline chemical reaction of condensation between SiO2and AlO2monomers. Such a matrix can retain a large number of cations to compensate for the Al+3in place of Si+4in the tetrahedra. Arsenic-rich mine tailings from a gold mining site were activated with NaOH solution and commercial Na-Silicate (Na2O/SiO2= 3) to produce a no-hazardous final material. Granulated blast furnace slag and metakaolin were used as co-binders to optimize the formulations. Leaching test was used to evaluate the inertization capability of the matrix after curing times of 7 and 28 days. The leaching results show that increasing curing time there is a significant decrease of As leaching due to the better consolidation of the material. Leaching of Cu, V, Ba and Zn significantly decrease, while Ni and Cr remain almost constant and Sb slightly increases

New insights into phenol and polyphenol composition of Stevia rebaudiana leaves

The diversity in phenols and polyphenols of stevia leaf has been simplified applying sequential fractionation techniques on its ethanol extract through ultrasound assisted maceration. Two of the fractions obtained by reverse-phase column chromatography resulted differently active in an extensive antioxidant and cytotoxic screening. Both fractions were chemically profiled by ultra-performance liquid chromatography (UHPLC) coupled with electrospray ionization (ESI) quadrupole/time-of-flight (QqTOF) mass spectrometry (MS). One of the fractions was composed mainly of chlorogenic acids and flavonol triglycosides, whereas the other was rich in flavonoids mono- and diglycosides and in their hydroxycinnamoyl derivatives. Among the fifty compounds identified, non-phenol metabolites, such as benzyl primeveroside and roseoside, as well as a lignan polyphenol (5'), are reported for the first time as constituents of the Stevia leaf.The diversity in phenols and polyphenols of stevia leaf has been simplified applying sequential fractionation techniques on its ethanol extract through ultrasound assisted maceration. Two of the fractions obtained by reverse-phase column chromatography resulted differently active in an extensive antioxidant and cytotoxic screening. Both fractions were chemically profiled by ultra-performance liquid chromatography (UHPLC) coupled with electrospray ionization (ESI) quadrupole/time-of-flight (QqTOF) mass spectrometry (MS). One of the fractions was composed mainly of chlorogenic acids and flavonol triglycosides, whereas the other was rich in flavonoids mono- and diglycosides and in their hydroxycinnamoyl derivatives. Among the fifty compounds identified, non-phenol metabolites, such as benzyl primeveroside and roseoside, as well as a lignan polyphenol (5'), are reported for the first time as constituents of the Stevia leaf. (C) 2018 Elsevier B.V. All rights reserved

Drug release of hybrid materials containing Fe(II)citrate synthesized by sol-gel technique

The use of oral iron integration is commonly recommended for the treatment of iron deficiency, nevertheless the diagnosis and treatment of this disease could clearly be improved. The aim of this work was the synthesis of therapeutic systems, iron (II) based, by sol-gel method. In an SiO2 matrix, we embedded different weight percentages of polyethylene glycol (PEG6, 12, 24 wt%) and ferrous citrate (Fe(II)C5, 10, 15 wt%) for drug delivery applications. Fourier Transform Infrared (FTIR) spectroscopy was used to study the interactions among different components in the hybrid materials. Release kinetics in a simulated body fluid (SBF) were investigated and the amount of Fe2+ released was detected by Ultraviolet-Visible spectroscopy (UV-VIS) after reaction with ortho-phenantroline. Furthermore, the biological characterization was carried out. The bioactivity of the synthesized hybrid materials was evaluated by the formation of a layer of hydroxyapatite on the surface of samples soaked in SBF using FTIR spectroscopy. Finally, also, the potential antibacterial properties of the different materials against two different bacteria, E. coli and P. aeruginosa, were investigated

Alkali activation as new option for gold mine tailings inertization

Abstract The mining industry produces a huge quantity of sulphidic mine tailings, which cause several short- and long-term environmental problems when disposed by landfilling in impounding lakes. The possibility of immobilizing several heavy metals from gold mine tailings by reactive geopolymerization technique has been investigated in the present study. The chemical stability of geopolymers synthetized by the alkali activation of metakaolin and blast furnace slag and the addition of 40–50 wt% gold mine tailings is demonstrated. The geopolymers were cured at room temperature, and the effects of different Si/Al and Na/Al molar ratios and curing times were investigated. The inertization effectiveness was evaluated by means of leaching tests carried out according to standard EN 12457 after 7 and 28 days and after 18 months. The samples were immersed into the water for 1 day, and the leachable metals in the test solution were determined by ICP-OES. The results show that various elements (Cr, Cu, Ni, Zn and Mn) from gold mine tailings are able to immobilize almost completely by alkali activation with proper co-binder material. The immobilization efficiency were highly improved with longer curing period also for the problematic elements As, V, Sb and B

Strategies for immobilizing homogeneous zinc catalysts in biodiesel production

This work describes two strategies for immobilizing Zn(II) catalysts: anchorage of a [ZnCl2(N,N)] type complex on silica and decoration of PAMAM-G0-3 dendrimers with analogous metal pendants. Both types of catalysts were able to catalyze the trans-esterification of neutral and acid soybean oil, and could be easily recycled through filtration techniques.The authors thank MIUR for financial support (PON 01_01966 Enerbiochem).Peer Reviewe